A conventional liquid-treating apparatus using a high-voltage pulse discharge is described in, for example, JP 2009-255027 A. FIG. 10 shows a configuration view of a conventional sterilizing apparatus described in JP 2009-255027 A.
The sterilizing apparatus 1 shown in FIG. 10 comprises a discharge electrode 6 including a pair of a columnar high-voltage electrode 2 and a plate-shaped ground electrode 3. The high-voltage electrode 2 is covered with insulator 4 except for an end face of a tip portion 2a, to form a high-voltage electrode portion 5. The tip portion 2a of the high-voltage electrode 2 and the ground electrode 3 are opposed to each other with a predetermined gap, being immersed in to-be-treated water 8 within a treatment vessel 7. The high-voltage electrode 2 and the ground electrode 3 are connected to a power supply 9 which generates high-voltage pulses. The discharge is made by applying negative high-voltage pulses of 2 kV/cm to 50 kV/cm and 100 Hz to 20 kHz between both electrodes. Bubbles 10 of steam and a jet flow 11 caused by bubbles 10 are generated by evaporation of water with energy of discharge and vaporization involved by a shock wave and a jet flow 11 is generated by the bubbles 10. Plasma generated around the high-voltage electrode 2 generates OH, H, O, O2−, O−, and H2O2 to destroy microorganism and bacteria.
Similarly, JP 2007-207540 A proposes a method for purifying liquid wherein the liquid is boiled and vaporized to form bubbles and ionize the vaporized substance (generate plasma) within the bubbles to form ions and the ion species in the plasma are penetrated and diffused in the liquid. JP 2007-207540 A describes that, in order to generate plasma, high-voltage pulses having a maximum voltage of about 1 kV to 50 kV, repeated frequencies of 1 kHz to 100 kHz and a duration of 1 μs to 20 μs, are applied to an electrode pair of high-voltage electrodes.
Another conventional liquid-treating apparatus is described in JP 2000-93967 A. JP 2000-93967 A discloses that a liquid-treating apparatus described in this document can reduce an applied voltage by interposing bubbles, which are supplied from outside, between electrodes in liquid, whereby power consumption can be reduced. Similar techniques are disclosed in JP 2003-62579 A and JP 2010-523326 A and JP 3983282 B.